Miniature thermostatic switch



Feb. 25, 1969 R. 'r. AUDETTE 3,430,177

MINIATURE THERMOSTATIC SWITCH Filed Dec. 30. 1966 Sheet 0f 2 INVENTOR Richard T.Aude'ffe BY fXA 8.1L)?- ATTORNEY Feb. 25, 1969 R. T. AUDETTE 3,430,177-

MINIATURE THERMOSTATIC SWITCH Filed Dec. 30, 1966 Sheet United States Patent Claims ABSTRACT OF THE DISCLOSURE Miniature thermostatic switches, particularly snap acting which employ an electrically conductive can electrically isolated from and sealed to an electrically conductive lid by means of an electrically insulating adhesive gasket. A thermostatic element and movable contact are mounted on either the can or the lid while a stationary contact is mounted on the other of the two parts. A stop may be provided to limit travel of the thermostatic element and in one embodiment flanges on the housing are bent over to clampingly engage the cover member to facilitate bonding of the lid to the can. A plurality of weld projections are provided in the lid to permit different orientation of the lid and terminal attached thereto relative to the housing. An electrically insulating sleeve is provided to electrically isolate the switch from its environs.

Background 0] the invention In the operation of motors, generators, transformers and other electrical apparatus, it is desirable to protect the windings and other parts thereof from excessive currents and heating. Circuit breakers installed in the current paths of such apparatus are normally for protection from over-currents within the apparatus and do not necessarily protect it against overheating due to continuous operation, high currents, or other causes. To adequately guard the safety of the apparatus, it is necessary that the protective device be placed within the apparatus to assure close monitoring. With the trend toward miniaturization of motors, transformers and generators and the like, it is necessary that protective devices be also miniaturized, at least to the extent that they may be placed within the apparatus.

It is, therefore, an object of the invention to provide a thermally responsive switch that may be easily installed within the windings of electrical apparatus.

Another object is to provide a switch which is inexpensive to construct, dependable in operation, and which consists of a minimum number of parts.

Another object of the invention is to provide a switch that may be easily calibrated.

It is still another object of the invention to provide a miniaturized thermostatic switch of which the parts thereof are suitable for mass production techniques.

Yet another object is to provide a miniature switch which is sealed to prevent entrance of air, dust and liquid which can deleteriously affect operation of the switch.

Other objects and features of the invention will become more readily understood from the following detailed description and appended claims, when read in conjunction with the accompanying drawing in which like reference numerals designate like parts throughout the figures thereof.

Brief description of the drawings FIGURE 1 is a pictorial view of the switch according to the invention;

FIGURE 2 is an exploded view showing the various parts of the switch;

FIGURE 3 is a cross-section taken along section line ice 3-3 of FIGURE 1 showing an end view of the switch in its closed position; and

FIGURE 4 is a cross-section taken across section line 44 of FIGURE 1 showing a cross-section of the switch along its length, the figure showing the switch in a closed position in solid lines and in an open position in dotted lines.

FIGURE 5 is a top plan view of a second embodiment of the invention with sleeve 60 partly broken away;

FIGURE 6 is a cross section taken on line 6-6 of FIGURE 5;

FIGURE 7 is a cross section taken on line 7--7 of FIGURE 6;

FIGURE 8 is a pictorial view of lid 50 used in the second embodiment.

Description of the preferred embodiments Referring now to the drawings, FIGURES 1 and 2 show the switch 1 as comprising the lid 10, the spacer gasket 11, the thermostatic member 13 and the can 12. As shown more particularly in FIGURE 2, the lid 10 is made of metal, preferably stamped to a rectangular configuration with a lobe 15 having a hole 16 therein for attaching a lead wire from the apparatus to be protected, and a depressed center section 10a.

To the underside of the lid 10 in the depressed center section 10a is welded one end of a curved, snap-acting bimetallic strip member 13 having a contact 14 at its other end. This strip member is not welded at its end directly to the plate in the embodiment shown, but is held to a spacer 20 (FIGURES 3 and 4) by weld button 21 extending through the strip. Although a spacer 20 is used in the specific embodiment, as already stated, a depression formed in the lid 10, similar to indent 19 in the can 12, would function equally well as a spacer to keep the free end of the contact member 13 physically separate from the lid.

The metallic can 12 has a flange-like portion 22 extending around its periphery for mating with the flange-like portion 23 of the lid 10. Contact to the can is provided by the way of lobe 17 having hole 18 therein. At the bottom of the can and at a location predetermined for registry with contact 14 at the free end of the bimetallic member 13, is the raised indent 19 having a contact 19a thereon for engaging said contact 14 in the closed position of said member 13. The lid 10 and the can 12 are joined by the gasket 11 which electrically isolates the lid from the can, said gasket joining the two members by engaging their respective flanges. The gasket may be, for example, of Mylar and coated on each side with a thermosetting adhesive material. After the parts have been assembled and properly joined, pressure is applied to the lid 10 and the assembly heated to a temperature sufficient to cure the thermosetting adhesive, but not high enough to deleteriously affect the calibration of member 13, bonding the lid to the can. This method of sealing the parts not only provides good electrical isolation and a tight bond, but also a simple means of fastening the parts without the use of screws or rivets.

In FIGURES 3 and 4, the position of the bimetallic member 13 is shown in relation to indent 19 and contact 19a thereon after the lid 10 is joined to the can 12. When in position, contact 14, secured to the free end of bimetallic member 13, extends down toward the bottom of the can 12 and engages the contact 19a, which serves as the other contact for the switch. As shown in solid lines, the switch is in the ON position, providing a direct electrical path between terminals 15, through spacer 20, bimetallic member 13, contact 14, contact 19a, and terminal 17.

Member 13 is a composite strip made up of two or more metals having different thermal coefficients of expansion, so that a change in temperature will cause unequal expansion and contraction of the opposite faces of the strip. The strip is shaped to have a cupped portion, as for example by forming a spherical projection into one face thereof. Thus shaped and constructed, it will be found that, upon raising the temperature, the unequal expansion of the metals constituting the strip will tend to flatten the cupped surface until, at a predetermined temperature, a sudden reversal of flexure of the shape of the strip occurs in the opposite direction, which reversal of shape or flexure will be maintained until the temperature is substantially lowered, at which time, the thermostatic member 13 will suddenly return to its initial shape. In both of these movements, the reversal of curvature is exceedingly abrupt, and is caused by the expansion or contraction of the metals of which the thermostatic member is composed.

To calibrate the switch and insure that it will function within the desired operating range, indent 19 is forced upward by applying pressure to the bottom of the can 12 until the contact 19a engages contact 14. Additional pressure is then applied to place an upward force on the thermostatic member 13.

In the above embodiment, contact 14 remains in contact with the contact 19a as the temperature rises until reversal or curvature occurs in member 13. At that time, contact 14 breaks with contact 19a and opens the circuit to the apparatus being protected.

In many bimetallic members, such as member 13, there is a condition which is called creep. As the temperature rises, the member slowly begins to distort and move up slightly until reversal of curvature occurs. If a slight additional pressure is not applied by indent 19 upon contact 14 through contact 19a (and therefor upon member 13), there will be a tendency for the contact 14 to creep away from contact 19a breaking contact before the critical temperature is reached. However, if an upward pressure is applied on member 13 beyond the pressure necessary for contact 14 to engage contact 19a, contact between 19a and contact 14 will be maintained until reversal of curvature occurs. In this manner, the breaking temperature of the member 13 may be adjusted by the extent to which indent 19 extends upwardly to engage contact 19a with contact 14.

Since both the can 12 and the lid 10 are electrically hot, they must be insulated from all metallic surfaces. This may be done by surrounding the switch with a heat shrinkable insulating tubing or encapsulating it in several varieties of epoxy resins available in the market.

Due to the adhesive bond between the lid and the can, the switch may be immersed in such media as motor winding varnish or pitch of the kind used in fluorescent light ballast, without having the inside of the switch contaminated.

In FIGURE 4 the open position of the switch is shown by dotted lines. It may be noted that the thermostatic member 13 may strike the underside of the lid 10. This may be used to advantage to limit the travel of the member, thus increasing its useful life.

FIGURES -8 show another embodiment of the invention in which the thermostatic member 40 is mounted on the bottom wall 34 of can 32. Thus the can serves as a protective enclosure for the thermostatic member preventing harm through careless handling of the device during assembly thereof. Projection 38 is formed in bottom wall 34 to provide spacing means on which to cantilever mount thermostatic member 40 by means of weld button 42 in a manner known in the art. Contact 44, of conventional contact material, is mounted on the free end of member 40. Dimple 36 is formed in wall 34 and serves as a stop member to prevent overtravel of the contacts. Stop 36 is so positioned that the extended are formed by the center of gravity of contact 44 as the member 40 snaps would pass therethrough.

Flanges 48, 48 and 49, 49 are formed in opposite side walls 46 respectively of can 32. Flanges 49 are of an extended length for a purpose to be described infra.

Gasket 51 of the same adhesive electrically insulative material as gasket 11 shown in FIGURES 14, is interposed between flanges 48, 49 and lid 50. Lid 50 is formed of an electrically conductive material and mounts thereon a stationary contact 54. Movable contact 44 on thermostatic member 40 is movable into and out of engagement with stationary contact 54.

Flanges 49 are bent over to clampingly engage lid 50. As best seen in FIG. 7 gasket 51 extends inwardly beyond bent over flanges 49 thereby maintaining the electrical isolation of lid 50 from can 32. This construction lends itself more readily to mass production techniques than the embodiment depicted in FIGS. 1-4 in that a separate fixture need not be furnished to hold the lid and can together while thermosetting adhesive is heated and cured to effect a bond among the parts, i.e., the bonding operation can be effected on the conveyor line while in motion through a heated zone by use of the clamping action of flanges 49. A good bond between the lid and can members is required to prevent seepage of varnish or other media which would deleteriousl affect the calibration and operation of the switch. This embodiment results in an especially effective bond since tthe required pressure can be maintained for a longer period of time using mass production techniques than if a separate fixture had to be provided as in the FIGS. 1-4 embodiment.

FIGURE 8 shows a feature which gives added flexibility to switch 30. Two sets of weld projections are provided, 52a and 52b respectively for attaching fixed contacts 54. This permits terminal orientation, as best seen in FIG- URE l, in which projections 5211 are employed or alternately a terminal orientation thereto by employing projections 52b. Gripping means 56 are provided on both lid 50 and can 32 for attaching leads L and L Switch 13 may be telescopically inserted in an electrically insulating sleeve member 60 to electrically isolate it from the environs in which it is placed as described supra.

Although the present invention has been shown and illustrated in terms of specific preferred embodiments, it will be apparent that changes and modifications are possible without departing from the spirit and scope of the invention as defined in the appended claims.

In the claims:

1. A thermostatic switch comprising an electrically conductive can having a bottom wall and upstanding side walls forming a cavity therein; an outwardl extending flange attached to the free ends of the side Walls; a thermostatic member cantilever mounted on said bottom wall, the side walls extending beyond said thermostatic member; an electrically conductive lid received on said flange and closing said can; an electrically insulative gasket adhesively interposed between said flange and said lid; said flange on at least two sides bent to clampingly engage said lid through said gasket; a stationary contact mounted on said lid; a movable contact mounted on said thermostatic member and movable into and out of engagement with said stationary contact; and terminals attached to said lid and said can.

2. A switch as defined in claim 1 in which said bottom wall is provided with a stop member to limit the travel of the thermostatic member when said movable contact moves out of engagement with said stationary contact.

3. A switch as defined in claim 1 in which said lid is provided with two sets of weld projections, the stationary contact welded to one of the two sets of weld projections, thereby permitting 180 displacement of the lid terminal relative to said can.

4. A switch as defined in claim 1 in which a spacer is provided on said bottom wall for mounting said thermostatic member thereon.

5. A switch as defined in claim 1 in which an electri- 5 6 cally insulative sleeve member is provided for reception FOREIGN PATENTS therein of said switch. 826,030 5/ 1956 Great Britain.

References Cited BERNARD A. GILHEANY, Primary Examiner. UNITED STATES PATENTS 5 R. COHRS, Assistant Examiner.

2,619,564 11/1952 Raleigh 00- US. Cl. X.R.

3,100,827 8/1963 Grimshaw 200--113 337380, 89, 112 

